The present invention relates to safety systems for detecting liquid contaminants in pneumatic lines and closing the lines in response thereto and, more particularly, to safety systems in pneumatic control lines which control valving associated with liquid delivery systems such as automated paint spray apparatus.
In a liquid delivery system such as a pneumatically controlled robotic paint spray system, low pressure air lines share valve interfaces with high pressure liquid containing lines delivering paint to be sprayed. For example, in automated paint spray delivery systems the pneumatic control pressures are usually industrial air lines operating at or below 100 pounds per square inch (psi), and the liquid lines typically deliver paint and solvents at pressures in a range from 150 psi to 1500 psi.
The difference in pressure between the pneumatic and liquid lines may cause contamination of the pneumatic control system. If a defect occurs at one of the valve interfaces between the pneumatic and liquid systems, the greater liquid pressure will cause liquid to flow into and through the pneumatic lines. If left uncontrolled, this liquid flow would eventually fill the pneumatic lines and contaminate the entire pneumatic system, destroying all or most of the pneumatic control apparatus. Such a contamination problem is especially acute in automated systems, which are frequently unattended for extended periods of time, and in which a valving or interface defect could literally shut down and destroy an entire paint spraying station and thereby disable or render malfunctional one or more automatic paint spraying robots.
Moreover, in automated factories such as automobile plants, the problem of a malfunctioning paint spraying robot may be readily compounded into larger problems. If a robot fails to apply paint to the body of a car or a part thereof, that particular body or part may be mismatched with parts subsequently added further down the assembly line. Hence an entire car factory may be shut down because of a relatively minor defect in a paint spray valving system.